Hey Stackoverflow community :)
Im looking into making a camera stream video from a an RC device into a computer using wifi.
After considering all of the options I had Im left with two:
use UDP to transfer video in packets
use packet injection and packet sniffing on the receiving device.
I was wondering what are the pros and cons of each method (for that specific purpose of video transmission)?
after looking around I found many implementations for both ways but nowhere have they specified why one is better than the other.
few things that I have not mentioned:
I know UDP does not have error correction which can make the video weird- I dont care about the quality of the video as long as it will be recognizeable.
I dont want to use connection based protocol (TPC, etc)- I dont want to wait for handshake when I get disconnected.
thanks :)
I'm trying to do a similar thing. My take on this is basically when you use the wifi cards in monitor mode (i.e. using packet sniffing/injection) you don't actually need to be connected to that network. Typically, you still need to be connected to an Access point as a client then you can communicate using UDP through that connection. But, in this case, the UDP messages are routed to the Wifi cards and the packets are injected out without being associated with any client. Then, any 'client' just has to sniff or listen on that same channel to get the transmission. So the benefit is not only does UDP not check for lost frames/etc, but also in this case you don't need to be connected to the network to get the packets.
In my case, this is preferable, since basically you will need to connect to the AP in the former case and that would require more capable hardware on the receiver side typically (more range is needed for the association part since you need to send messages back over TCP essentially to get it connected).
FYI here are the links/repos I am using and it also is a reference to what I am talking about
https://docs.px4.io/master/en/tutorials/video_streaming_wifi_broadcast.html
https://github.com/svpcom/wifibroadcast
I am using an off the shelf 'solution' in the short term, the Accsoon Cineye Air, which basically transmits HDMI 300ft line of sight over WiFi. You need an android phone to receive it, and basically I'm using the Vysor application (paid version is $40) to mirror the screen to my desktop. It works, but the latency is still more than I want : 60ms at least from the cineeye, so you can drive it around but its not as quick as DJI which is around 30-40ms ), which is my goal.
Related
I want to capture and send some packets to the access point for testing purposes. I have the packet captures made via wireshark but I do not know how to proceed to be able to send these packets from my macbook.
I tried things like scapy, colasoft etc, but they do not seem to work as they require an external wifi adapter to be able to relay these packets outwards.
Two main questions:
Is it possible to send custom packets from macbook to a required access point. (Without using external network adapter).
If yes, what are some tooling/Scripting options that I can look at ? Any recommendations?
I am networking novice so please pardon me if the question is trivial. Thank you!
Your builtin Wifi adapter likely does not support Wifi injection.
You can check this by googling the Wifi chip that is within your computer (there are various methods to get that info depending on your OS) whether it supports Wifi injection or not.
So yeah, you'll likely need an external card (check the specs before buying it)
I am currently working with one of Growatt inverters, 5 KVA residential inverter, It has two ports one is RS-485 I have connected a Smart Energy Meter with it to control backpower flowing to grid, and on the other port Growatt wifi device was working, I wanted to use my own platform, I used this protocol Growatt PV Inverter Modbus RS-485 RTU Protocol and then connected wire to RS-232 with a Raspberry Pi to read the data and send it back to my server. Now the issue coming is as soon as both devices start to work then inverter starts showing an error. I cannot understand why it was not giving with the Growatt device. Is there any solution?
I want to ask some question about your problem to help you if I can :-).
Are you going to monitor inverter data on your server? If yes => so, why you don't connect your server to inverter directly (I mean by using USB to the RS-485 converter).
What is your connection type? If it is Modbus-RTU you need to find Modbus register map to get your desired data. You could find this in the inverter user manual.
Be careful about your Modbus communication configurations and settings (i.e. Baudrate, ID, Parity and Byte Size).
I'm trying to write a simple C code with WinPcap to broadcast a beacon packet and capture it in all nearby WiFi units. The code I'm using is very similar to the ones available at WinPcap[1].
The code runs fine if I create an ad-hoc network connection and join all the computers into it. However, this process of creating and joining to an ad-hoc network is cumbersome. It would be much better if, regardless of what network each computer is in, the beacon packets would be broadcasted and captured once the code is running.
As simple as this problem might sound, after some searching it seems that this is not possible to be done on windows (unless re-writing drivers or maybe the kernel):
Raw WiFi Packets with WinPcap[2]
Sending packets without network connection[3]
Does winpcap/libpcap allow me to send raw wireless packets?[4]
Basically, it would be necessary to use the WiFi in monitor mode, which is not supported in Windows[5]. Therefore, if the computers are not in the same network connection, the packets will be discarded.
1st Issue
I'm still intriguing, beacon and probe request packets are a normal traffic across the network. How they could be being sent and received constantly but the user is not allowed to write a program to do so? How to reconcile that?
2nd Issue
Does anyone has experience with Managed Wifi API[6]? I've heard that it might help.
3rd Issue
Acrylic WiFi[7] claims to have developed a NDIS driver which support monitor mode under Windows. Does anyone has experience with this software? Is it possible to integrate with C codes?
4th Issue
Is it possible to code such Wifi beacon on Linux? and on Android?
www.winpcap.org/docs/docs_412/html/main.html
stackoverflow.com/questions/34454592/raw-wifi-packets-with-winpcap/34461313?noredirect=1#comment56674673_34461313
stackoverflow.com/questions/25631060/sending-packets-without-network-connection-wireless-adapter
stackoverflow.com/questions/7946497/does-winpcap-libpcap-allow-me-to-send-raw-wireless-packets
en.wikipedia.org/wiki/Monitor_mode#Operating_system_support
managedwifi.codeplex.com/
www.acrylicwifi.com/
Couple questions I will try to answer. Mgmt and Ctrl packets are used for running a wifi network and don't contain data, I would not call these normal packets. Windows used to(I think still does) convert data packets into ethernet frames and pass it up the stack. Beacon and Probe Req pkts are not necessary for TCP/IP stack to work, ie. web browsers don't need beacon frames to get your web page. Most OS's need minimal info from mgmt/ctrl pkts to help a user interact with a wifi adapter, most mgmt/ctrl pkts only are useful to the driver(and low level os components) to figure how to interact with the network. This way the wifi adapters look and act like ethernet adapters to high level os components.
Never had any experience with Managed Wifi API or Acrylic, so can't give you any feedback.
Most analyzers that capture and send packets do it in 2-3 separate modes mainly because of hardware. Wifi adapters can be in listen mode(promiscuous mode and/or monitor mode) or adapter mode. To capture network traffic you need to listen and not send, ie. if someone sends a pkt while you are sending you miss that traffic. In order to capture(or send) traffic you will need a custom NDIS driver in windows, on linux many of them already do. Checkout wireshark or tshark, they use winpcap to capture pkts in windows and there are some adapters they recommend to use to capture pkts.
Yes it is possible to send a beacon on linux, ie. Aireplay. I know its possible to capture traffic on Android but you it needs to have rooted or custom firmware, which I would believe also means you can send custom pkts. If you are simply trying to send a pkt it might be easier to capture some traffic in tshark or wireshark and use something like aireplay to resend that traffic. You could also edit the packet with a hex editor to tune it to what you need.
I have a live video chat application and I use a TURN server which supports STUN/TURN and both UPD/TCP transmission.
Sometimes users can be connected to the network which blocks that much ports and protocols that WebRTC connection just cannot happen (usually those are corporate networks). I would like to check if a WebRTC connection is possible before users try to connect to each other (actually, perform a technical check).
How can I do it? Ideas I have in my head:
Try to download a hosted chunk of data (audio file, for example) via WebRTC - is it possible and would this be enough to make sure both inbound and outbound connections are open?
Use a TURN server as a host to make a connection to and see if it fails (have no idea if I can do it or not)
Use Flash to try to download/upload a chunk of data over specific ports and protocols. May be even using Cirrus. However, I am not sure this test will be accurate from WebRTC prospective.
Any other ideas?
Additional requirement: the checking technique must support Chrome, Opera and Firefox. Preferably also IE/Safari via Temasys plugin.
Edition 1 - gathering ICE candidates is a good idea, however, it is not 100% reliable. Once I checked logs in my application and it actually gathered relay ICE candidates, but video/audio transmission failed. Tested on Apprtc as well and got same results.
The best way to check is to connect with just a data channel first. Your users won't notice. If that works then audio and video are almost guaranteed to work. As a bonus, you can use the data channel for signaling for super-fast connecting when your users are ready.
the typical WebRTC approach to this is to create a peerconnection with STUN and TURN servers, call createOffer and setLocalDescription and watch the candidates gathered. See e.g. http://webrtc.github.io/samples/src/content/peerconnection/trickle-ice/
If you get srflx candidates, your stun server works (i.e. UDP is not blocked). More interesting is whether you get relay candidates. If you do, using TURN as a fallback will work. Quality might suffer if TURN/TCP is used. If you don't get relay candidates... calls are very unlikely to work.
I want to implement a demo application to listen data via TCP/IP.
Data Transmitter will transmit a series or ASCII char or a series of string all the time. It feeds data into TCP/IP address (eg. 127.0.0.1:22) This could be a GPS transmitter.
I want to implement a demo application for receiving data by clicking the start button and listening to the data via TCP/IP and display it accordingly.
Correct me if I am wrong, I don't think I can use Server/Client server for this purpose. I tried to create a client application with TIdTcpClient, it receives only one time data. I don't think Indy has a TCP listening component.
Thanks in advance.
If you wanna monitor network comunications between some device and some other program on your computer using of TIdTCPServer won't work. Why? Once Indy will read network data it will mark it as processed and delete it from network buffer. So that data probably won't even reach to the other program on your computer. Workaround for this is that you design your application to actually work similar as network bridge. Your application listens to the data on one port and then forwards that data on another port on which the other program is listening. But the main problem is that you have to make this to work both ways.
What you need is somekind of a component which is able to peek at the network data but don't interact with it. This is usually done on driver level.
Now if it is not abolutely necessary to have such functionality in your own software but you are only interested in getting the data I recomend you try Wireshark (http://www.wireshark.org/). Wireshark is a verry powerfull freware software which alows you to monitor all netwrok traffic on basically all protocols without causing any interuptions. In order for this software to work it instals special driver which serves for intercepting the network data.
Maybe you would want to use same driver in your application if this functionality needs to be in your application.
Based on your diagram I think that your implementation could also be based on a message-oriented middleware, using a message broker which receives the GPS transmitter or other data.
The message broker would then store the data internally and forward it to all interested clients which are connected. A typical messaging pattern in this case is a "Topic", which broadcasts the messages similar to a radio station.
So the middleware will ensure that the information will be collected (optionally also persisted to disk) and then guarantees the delivery to the receivers. This can be done even in a way where receivers which have been off-line for a while still receive the GPS messages created while they where not listening ('retroactive consumers').
There are many popular free open source message brokers, and most of them also can be used with Delphi.